170 JOURNAL OF ECONOMIC ENTOMOLOGY [Vol. 4 



that each winged Aphis normally produces eight young, of which four 

 are males and four females, but in their laljoratories they succeeded 

 in getting only three to six. 



The cytological studies of von Baehr, Volume III, 1909, in the 

 "Archiv fiir Zellforschung" under the title of "Die Oogenese bei einigen 

 viviparen Aphididen und die Spermatogenese von Aphis saliceti, 

 mit besonderer Berlicksichtigung der Chromatinverhaeltnisse, " con- 

 tain valuable facts on the development of true sex forms in Schizoneura- 

 lanigera. The more important points of that part of his paper bearing: 

 on our problem are here given. 



Von Baehr removed the embryos from very young nymphs. The 

 nymphs were just showing the wing pads, and the embryos removed 

 from them were, therefore, of the kind regularly developing into true 

 sex forms. Sections of the ovaries of these embryos of true females 

 were compared with sections of ovaries taken from agamic embryos 

 in the same stage of development. At this stage the ovaries of the 

 two forms were exactly alike. 



In embryos taken from somewhat older nymphs he found that most 

 of the ovarian tubes contained parthenogenetic eggs, while two of them 

 develop into winter ovaries. Of these two, only one is fully developed, 

 the other ovary with its egg is spoiled before maturity. This explains 

 the process by which only one egg is produced by the true female, 

 whereas all the other forms give birth to more than one young. 



Mr. Symons: I would like to ask Mr. Hunter what was the per cent 

 of Aphids at the beginning of the season? 



Mr. Hunter: About 90 per cent. We cleared a total of 70 per 

 cent clean trees, about 20 per cent with knotty rootlets and about 

 10 per cent that had Woolly Aphis present on them after the 

 season's treatment. 



Mr. Symons: You had different blocks? 



Mr. Hunter: Of two-year stock. 



Mr. Symons: I tried tobacco dust and lime-sulfur on some two- 

 year-old trees and got the best results with tobacco dust. It was 

 put on very carefully. 



President Sanderson: The next paper will be presented by 

 Mr. A, G. Ruggles. 



